This research is directed toward the development of the experimental and mathematical techniques required for the application of the nuclear magnetic resonance-lanthanide shift reagent method to the determination of molecular conformations in solution. The method is being used to study the conformations of a number of substituted diphenyl ethers which are structural analogs of the thyroid-active thyronines. A complex is formed in solution between a lanthanide shift reagent and a conformationally rigid, bicyclic organic substrate, which is connected to a conformationally flexible substituent (e.g., a diphenyl ether). The nmr-lanthanideinduced shift data for the bicycle substrate, together with the three dimensional structure of the substrate from X- ray crystallographic data, permits the determination of the lanthanide- substrate structure in solution. This data and the shift for the flexible substituent permit a conformational analysis to be made of the substituent. We have evaluated several bicyclic frameworks and performed conformational analyses for phenoxy and diphenyl ether substituents.